Body Composition Tracking
Overview
Body composition tracking is a longitudinal phenotyping protocol that combines regular body weight measurements with non-invasive nuclear magnetic resonance (NMR) relaxometry to quantify lean mass, fat mass, and free fluid compartments in live, conscious rodents over the course of an experimental intervention. Unlike terminal methods such as dual-energy X-ray absorptiometry (DEXA) or chemical carcass analysis, time-domain NMR allows repeated measurements in the same animal within minutes, enabling within-subject tracking of adiposity changes with a precision of approximately 0.5 g for fat mass and 1.0 g for lean mass. The protocol establishes baseline body composition before intervention onset and tracks changes at weekly or biweekly intervals, providing the statistical power to detect subtle shifts in lean-to-fat ratio that would be obscured in cross-sectional terminal studies.
The primary metrics include absolute and relative fat mass (as a percentage of total body weight), absolute and relative lean mass, the lean-to-fat ratio, and rate of change for each compartment over time. These metrics are essential for metabolic phenotyping of diet-induced obesity models, genetic knockouts affecting lipid metabolism or appetite regulation, and pharmacological interventions targeting weight management. Body weight alone is insufficient because isocaloric interventions can produce reciprocal changes in lean and fat compartments that cancel in total weight, masking biologically meaningful phenotypes that body composition analysis reveals.
ConductMaze integrates body composition data from NMR instruments with concurrent food intake, wheel running, and metabolic cage measurements to provide a unified longitudinal dashboard of energy balance. The software automatically calculates body composition derivatives including fat mass accrual rate, lean mass preservation index, and adiposity index, and flags animals whose composition trajectories deviate from group means by more than two standard deviations. Terminal organ weight data (liver, gonadal fat pad, brown adipose tissue, spleen) can be appended to the longitudinal record for endpoint calibration and cross-validation with in vivo NMR estimates.
Trial Flow
Baseline Body Weight
Weigh each animal on a precision balance at the same time of day; record to nearest 0.1 g
NMR Baseline Scan
Place conscious animal in NMR tube for 90-second scan to obtain baseline fat mass, lean mass, and free fluid values
Intervention Onset
Begin experimental manipulation: diet change, drug administration, exercise access, or genetic induction
Weekly Monitoring
Repeat body weight and NMR scan at consistent weekly intervals throughout the study duration
Trajectory Assessment
Evaluate whether fat or lean mass trajectories differ between groups using repeated-measures analysis
Terminal Organ Collection
At study endpoint, collect and weigh individual fat depots, liver, and other organs of interest
Data Integration
Merge longitudinal NMR data with terminal organ weights, food intake, and metabolic records into a unified dataset
Study Completion
Archive complete body composition trajectory with per-animal growth curves and statistical summaries
Parameters
| Parameter | Type | Default | Description |
|---|---|---|---|
| Measurement Interval | duration | 604800 | Interval between body composition measurements in seconds (default 7 days) |
| Study Duration | duration | 6048000 | Total study length in seconds (default 10 weeks) |
| NMR Scan Duration | seconds | 90 | Duration of each NMR relaxometry scan in seconds |
| Weighing Time | enum | 09:00 | Time of day for body weight measurements to minimize circadian variability |
| Diet Type | enum | chow | Diet provided during the study: chow, high_fat_60pct, high_fat_45pct, western, or custom |
| Fasting Before Weigh | enum | no | Whether animals are fasted before measurements: no, 4h, 6h, or overnight |
| Terminal Organs Collected | enum | standard | Organ set: standard (gWAT, iWAT, BAT, liver) or extended (adds muscle, spleen, kidney) |
| Deviation Alert Threshold | float | 2.0 | Number of standard deviations from group mean to trigger automated welfare or phenotype alert |
Metrics
| Metric | Unit | Description |
|---|---|---|
| Body Weight | g | Total body weight measured on precision balance |
| Fat Mass | g | Absolute fat mass measured by NMR relaxometry |
| Lean Mass | g | Absolute lean mass (muscle, bone, organs) measured by NMR relaxometry |
| Adiposity Index | % | Fat mass as a percentage of total body weight |
| Lean-to-Fat Ratio | ratio | Ratio of lean mass to fat mass indicating overall body composition balance |
| Fat Mass Accrual Rate | g/week | Weekly rate of fat mass change calculated from longitudinal trajectory slope |
| Lean Mass Change | g/week | Weekly rate of lean mass change indicating muscle gain or wasting |
| Gonadal WAT Weight | g | Terminal gonadal white adipose tissue depot weight |
Sample Data
| Subject | Diet | Week | Body Weight (g) | Fat Mass (g) | Lean Mass (g) | Adiposity (%) | Lean:Fat Ratio |
|---|
Representative data for illustration purposes. Actual values will vary by species, strain, and experimental conditions.
Applications
- 1Diet-induced obesity phenotyping — quantifying fat mass accrual, lean mass preservation, and adiposity trajectories across high-fat and control diets
- 2Anti-obesity drug evaluation — measuring dose-dependent reduction in fat mass with concurrent monitoring of lean mass to distinguish fat-specific from catabolic effects
- 3Genetic metabolic phenotyping — characterizing body composition in knockout and transgenic models affecting lipogenesis, lipolysis, appetite, or energy expenditure
- 4Aging and sarcopenia — tracking age-related shifts in lean-to-fat ratio to model sarcopenic obesity and evaluate interventions promoting lean mass retention
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